In many cultures, an animal living underground jumps around and shakes the ground. In Mexico, it was thought that this animal was a jaguar. In Crete, it is the Bull of Knossos. Russia also had a bull. In Kamchatka, an Asian peninsula, it was a dog. An Indian story included a romping elephant.
The theme of animals that carry the earth is a common one. Siberian folklore says that a god named Tuli carried the earth on a dogsled. Unfortunately, the dogs had fleas and often scratched, causing the earthquakes. Some Native Americans thought that the earth was carried by a large tortoise. Whenever he took a step, the earth shook. Mongolians once believed that the world sat on the back of a frog. The frog would stumble, rattling his load. In West Africa, it was popularly thought that a giant carried the earth on his head. All of the plants were his hair, and all of the people and animals were insects that crawled through his hair. The earth shakes whenever he turns his head.
Other cultures have enlarged this type of story to include many animals that share the burden of carrying the earth. In India, four elephants hold the earth. A turtle holds the elephants. A cobra holds the turtle. If any of these creatures move, there's an earthquake. In East Africa, a fish carries a stone on its back. A cow stands on the stone, holding the earth on one horn. When the cow's neck starts hurting, she tosses the earth to her other horn, starting the quake.
Other countries developed more complex stories. In Japan, a giant catfish thrashing about was responsible for starting earthquakes. Usually, the fish was pinned down by a huge boulder, but when the gods went away in October he could get loose and cause disaster. When the gods came back, their leader carried a big rock to hold the catfish down again. In Chile, earthquakes were attributed to two snakes. One snake dug holes in the earth to store water in, but the other snake filled them in with stones. This caused the reptiles to fight, which caused the tremors. In Norse myth, the naughty god Loki was punished for killing Baldr by being tied to a rock. Overhead, a poisonous snake dropped poison onto his head. His wife stood next to him with a bowl to catch the poison when it fell, but occasionally she would have to empty it. When this happened, the snake's venom would drip onto him and he would struggle to free himself, beginning the earthquake.
Now we know that earthquakes are caused by tectonic plates rubbing together. Although these plates are always moving, when the stress on the rock overcomes the friction, the energy travels in waves along the earth's surface. The lines where the plates meet are called faults, and most earthquakes happen along them. In California, the line is called the San Andreas Fault. (If you're visiting California and get in trouble, a good excuse is "It's not my fault -- it's San Andreas' Fault!" But that's rather off-topic.) If you were living in ancient times and couldn't use science to prove things, what legend do you think you would have come up with?